A corporatiojsr of north caro



[STA 7 improved method of preparing paving masubstances otidifierent grades as'to size, those commonly muse runnlng from dust up to any closed as applied to bituminous paving materials, although itwill be understood that toinclude any materials to which the method iapplica'tionis a'continuation in part'of -'copending- United States application, Serial suitable binder,- which binder, in the case of bituminous mixtures,-is any suitable mineral cific manner of mixing, it is not necessary to 'In 'thepreparation of these paving ma- Patented Aug. 26, 1930 wrnrram RAGLANII), or RALEIGH, ,nori rirfl CARIOYIIIINVA', Assis tch TO: noBER'r 7o.

LASSITER a co or aLEIGrLNo TH CABQL'INA, QORPORATIOIJ or NOBTHACA/RO-M LINA.

-j amnion OF IBREP ARIN N9 Drawing. I The present'invention relates to a new and terial, andg'ais here described, will'be disby reference to paving materials, I intend which have invented is applicable. This No. 78,700, filed December 81, l925. s "In the production-of paving materials, 1t is customary to mix the aggregate with a pitch; Obviously, binders other than mineral pitch could be used here the pavement was of -anon-bituminous type. The aggre-, gate ma take a variety of forms, but, in the bitulithic pavement, is made up of mineral appropriate size, as,ffors example, a one and. one-half inch mesh. This aggregate is mlxed in suitable proportions with the binder, and after 'a thorough intermixing, it is ready to belaid upon theiii'oundation to form the road- Way. Variousmethods' of compounding'and mixing the aggregates and thebinder have been" proposed and are n'owi'in use, but. the

prs'entmethod is not dependent on any s describein detail a particular method ofr'nix ing. Furthermore, since my method of pre-w 35 specific apparatus, illustration or description paring the mixture is independentof any of the apparatus-is unnecessary.

' t rials,'it' isimportant that-an intimate relation be brought about between the aggregate and the. binder, and'the more" completely the a ement can be produced. Failureto thoraggregate is coated and. impregnated with the binder, the more stablewill be the paving mixture,' and a more stable and wear-resisting ouglilyQ'coatand impregnate the aggregate with the binder will result inan uneven and faulty mixturdiwith portions of the 'aggrethe binder;-: -When suchflfaulty mixture J anemia filed February 23; i927, Serial No. 170,429;

disintegratiomf both- I under stress. of traflic and under attacks ofimoisture, will rapidly develop bad spots inlthewlaid 'materialfi-. Various 1 plans have been (suggested for overcoming the diflicultyxand securing the desiredintimate relationofflbinder and aggregate, one of which plans contemplates 'laid',the pavement is asaaaata because of flaws, due to poorly coated aggregate, and

subjectingthe batch or mass of aggregate i and binde'r,whil'e in process of mixing, to air pressure, greaterthan atmospheric pressure, a while it was goingthrough'the/mixer; The Y "difliculty with this iplan is that since the material" is in a state of agitation, pressure is s not effectiveon the moving particles it is s 'difiicult to maintain an effective. pressure in the mixer, and'the period during which ma -terial' 'is passing .throiighthe mixer is too short to give completely satisfactory results. My method contemplates the application of pressurelto a stable mass of the'mixture under such conditions that the particlesfof coated continued pressure for such period as- "will bring about the desired result,and by following' the method, a paving composition'iis produced inwhich a very complete and intimate application of the binder to th'e aggregate is (found, and the difliculties dependent uponw poorly prepared and insufficiently and to expand the particles so that they will be in a receptive condition for coating and the usual steps I and impregnated aggregate, while in a} state" ot-"rest, will"be subjected to a uniform and ed and graded into its sizes in'thecus'tomary Y manner. It may be, and preferably' isflhor- Y "oughly heated, to-elimin'ate" all; moisture impregnating with thebinderl; The aggr'egate-thus prepared is then mixed with the 'bind'erywhich, if a bituminous binder, 'ispre ferably hot.- This mixing may be done in any 'suitab'lemixing machineof the pug mill type, or rotary cylinder type, whichever may be r a preferred. I The mixing operation will continue until "the aggregate has been thoroughly coated as to all of its particleswith the binder, and this is the material which is now customarily taken and laid upon the roadway to form the pavement. In this condition, it gives reasonably good results, but I have discovered that its qualities, particularly its stability, can be materially improved by taking the batch from the mixer, depositing it, in a suitable mass, in a substantially airtight container, and subjecting it to a pressure reater than atmospheric pressure, for such length of time as may be necessary or desirable. Any ty e of container may be used, although, preferably, a container lnsulated against heat dissipation, so as to retain the batch at substantially the temperature at which itcomes from the mixer, is used. Such container may be insulated by any of the approved heat insulating methods now in use. After the batch has been deposited in this container, I introduce air under pressure, and one or more air inlets may be used.

The effect of the air under pressure upon the mixed mass underthe conditions above mentioned is to bring about a more even distribution of the bituminousbinding agent over the surfaces of the mineral aggregate, the better impregnation of the cracks and crevices in the mineral aggregate with the binding agent, and impregnation of the interstitial spaces in the mixture, especially with reference to that portion of the mixture which consists of small particles of sand and finely divided mineral matter in the nature of dust. In other words, there is not only an impregnation of the mineral aggregate itselt, but a forcing of the latter together so that the finer particles more nearly take their ideal position with reference to the larger. Moreover, due to the pressure, any small voids existing in the mass are rendered even smaller.

To obtain the most perfect result, I supply the container in which the mixture is deposited with a pressure gauge and initially introduce air into the container to a predetermined pressure. The result of the reaction described above is naturally a shrinkage in the mass and due to this shrinkage the predetermined pressure will correspondingly fall. After the pressure has fallen its maximum amount, I restore the original pressure and if the mass is allowed to stand this restored pressure will fall in view of the further shrinka e. Thus my process includes the steps oi introducing a predetermined pressure and subsequently restoring this pressure .as many times as necessary so that finally the original pressure will be retained. At this point it is evident that the ultimate degree of density has been obtained. Of course, with the variation of the binder or aggregate according to different conditions, difierent pressures will be .used, the correct pressure beingdetermined empirically. The use of a separate container for the application of pressure enables me to hold the mixture in its stable condition any length of time necessary to complete the process. This, of course, is a distinct advantage over applying pres sure in the mixer, since the work would be considerably impeded it this apparatus were subjected to long periods of inactivity. As against the use of pressure in the mixing process, I obtain the advantages or" density and thorough impregnation as described above. It is obvious that when themass is mobile as in the mixing process, the actual impregnation will be slight and the thorough relative arrangement of the particles entirely impossible.

I Another advantage of this method is that the material may be held in the insulated heat retaii'iing container for a considerable period of time, and yet will be in condition for use. ,v

Under ordinary methods, the material must be taken directly from the mixer and laid on the job, with no provision for maintaining a supply, which may be drawn upon for a considerable period after it has been placed in the insulated container. Furthermore, by my method of storing, the material, after it has been mixed. and subjected to pressure, may be tested, and if found necessary,can again be returned to the mixer for further treatment or correction as to its makeup.

This intermediate step of storing and treatin as distinguished from taking directely from the mixer and laying on the job, has,

therefore, the advantage, not only of securing a more complete impregnation of the aggregate by the binder, but also has the practical advantages of readily permitting tests before using the batch, and of establishing a base or supply, which may be drawn upon for a very considerable period after the mixture has been made and stored.

I claim:

1. The method of preparing paving mateo rial and the like, which consists in mixing aggregate and binder in the presence of heat,

transferring and storing the mixed mass in quiescent insulated condition, and subjecting it to a fluid pressure greater than atmospheric pressure.

2. The method of treating paving material and the like, which consists in subjecting a quiescent mass of mixed aggregate and binder to measured fluid pressure greater than at mospheric pressure, and restoring such pressure upon its fall due to shrinkage of the mass. 7

3. The method of treating paving material and the like, which consists in subjecting a stablemass of mixed aggregate and binder to measured fluid pressure greater than atmosperic pressure, andrepeatedly restoring such pressure upon its fall due to shrinkage of the mass until it remains constant.

4. The methodoftre'ating paving material and the like, which consists'in sub'ecting a stable mass of mixed aggregate and inder to a predetermined fiuid pressure greater than atmospheric pressure, permitting a'maximum loss of pressure due to shrinkageof the mass,

and restoring the original pressure.

5. The method of treating paving material and the like, which consists in subjecting a stable mass of mixed aggregate-and binder tov a predetermined fluid pressure greaterv than I atmospheric pressure, permitting a maximum 7 loss of pressure due toshrinkage ofthe mass,

restoring the original pressure, and repeating the treatment until the original pressure I is retained.

6. The method of preparing paving material which consists in mixing aggregate with a suitable binder in the presence'of heat, depositingthe treated mixture in a stable insulated mass, and subjecting the mass to a fluid pressure greater than atmospheric pressure. 7

7; The method of preparing paving mate-', rial and the like, which consists in mixing aggregate and a suitable binder, depositing the mixture in a quiescent mass, subjecting the mass to measuredfluid pressure greater than atmospheric pressure and restoring such pressure ,upon its fallldue to shrinkage 0 ,mass.

8. The method ofpreparing paving mate'- rial and the like which consists in mixing c aggregate and asuitable binder, de ositing the mixture in a quiescent mass, su jecting the mass tomeasured fluid pressure greater ting a maximum loss of pressure .due to shrinkage of the mass, and restoring th originalpressure. i l

10. The method of preparing paving material and the like which consists in mixing" aggregate and a suitable binder, depositing the mixture in'a stable mass, subjecting the mass to a predetermined fluid, pressure greater than atmospheric pressure, permitting the maximum loss of pressure due to shrinkage of the mass, restoringthe original pressure,

and repeating the pressure application until the original pressure is'retained.

Intestimony whereof I have hereunto set my hand.

the

WILLIAM v'r. RAGLAND. 

